A typical gas turbine is configured by a compressor, a combustor, and a turbine. The compressor generates high-temperature, high-pressure compressed air by compressing air taken in from an air inlet port. The combustor obtains high-temperature, high-pressure combustion gas by supplying fuel to the compressed air and causing the fuel and air to combust. The turbine is driven by this combustion gas, and drives a power generator coaxially connected to the turbine.
The turbine in this gas turbine is configured by a plurality of vanes and blades alternately disposed inside a casing along a flow direction of the combustion gas. The combustion gas generated in the combustor drives a rotor to rotate by passing through the plurality of vanes and blades, and thus drives the power generator connected to the rotor.
Incidentally, in the gas turbine, part of the compressed air compressed in the compressor is extracted and used to cool a turbine casing and the vanes. Further, after part of the compressed air is guided to the outside and cooled by an air cooler, this compressed air cools turbine disks and the blades. In this case, the air cooler cools the compressed air using feed water (cooling fluid) supplied from an exhaust heat recovery boiler, for example. In order not to cause the performance of the gas turbine to deteriorate, this turbine adopts a structure that inhibits the combustion gas from flowing through a gap (clearance) by minimizing the gap between tip ends of the blades and the inner peripheral surface of the turbine casing, to such an extent that there is no interference therebetween.
An example of such a gas turbine is disclosed in Japanese Patent No. 4488631B. A combined cycle power generation facility disclosed in Japanese Patent No. 4488631B is provided with an extracted air cooler that generates cooling air by exchanging heat between water heated in an economizer and compressed air extracted from a compressor, a bypass system that bypasses the extracted air cooler, and an adjustment valve that adjusts an amount of air flowing through a bypass pipe. In this combined cycle power generation facility, when a rapid change in load occurs at the plant, the air temperature is controlled by adjusting the amount of air.
Incidentally, when activating the gas turbine, the blades of the turbine rotate at a high speed, and at the same time, they are affected by the combustion gas from early on. As a result, tip portions of the blades elongate outward in the radial direction. On the other hand, since the turbine casing has a large thermal capacity, the amount of outward elongation in the radial direction is small therein. As a result, a clearance between the tip ends of the blades of the turbine and the inner peripheral surface of the turbine casing becomes small. In this case, if the clearance between the tip ends of the blades of the turbine and the inner peripheral surface of the turbine casing is set in accordance with the time at which the gas turbine is activated, this clearance becomes larger than necessary during steady operation of the gas turbine. As a result, a problem arises in which recovery efficiency of the driving force generated by the turbine deteriorates, and consequently, the performance of the gas turbine itself deteriorates. At this time, although the adjustment valve of the bypass system in the air cooler may be used as a control valve, when a driving source or a control signal is lost, a degree of opening of the adjustment valve cannot be retained. Thus, when the valve is fully opened, there is a risk that the cooling air temperature may rise and cause contact. Further, when the valve is fully closed, there is a problem that the cooling air temperature may fall and cause the clearance to expand, thus causing deterioration in performance.
In order to solve the problems described above, an object of the present invention is to provide a gas turbine that is capable of ensuring safety and improving performance by having an appropriate amount of clearance between a turbine casing and blades.